Digital image processing has become a significant form of image processing because of continuing improvements in techniques and increasingly powerful hardware devices. Digital image processing techniques have augmented and, in some cases, replaced methods used by photographers in image composition and dark room processing. For example, digital image processing techniques such as contrast balancing, edge sharpening, color balancing or retouching of defects are employed for editing original photographic images. Moreover, with the aid of a computer, digitized images can be edited to achieve a variety of effects such as changing the shapes and colors of objects and forming composite images.
Until recently, real-time editing of digital graphic images was feasible only on expensive high-performance workstations with dedicated, special-purpose, hardware. The progress of integrated circuit technology in recent years has produced microprocessors with significantly improved processing power and has also reduced the costs of computer memories. These developments have made it feasible to implement advanced graphic editing techniques in personal computers. These editing techniques, however, are typically complex and require an expertise beyond that of ordinary users of personal computers.
A common artifact found in a photograph of a person or animal, especially when a flashbulb without a preflash is used when taking the picture, is a red spot or halo obscuring all or part of the pupil of each eye. This artifact, commonly called a "red eye," is typically produced when the pupil is sufficiently dilated to allow a noticeable amount of light from a source light to reflect off the back of the eye. In humans, the reflection is typically a reddish color (hence the term "red eye"); however, it can be other colors including a green color in some animals.
Techniques are known for editing a digital image to remove a "red eye" effect. These techniques, however, require digital painting skills for covering the red eye area with a corrected image of the pupil area. Normally, the pupil area of the eye does not comprise a single color, nor does it have a constant brightness. Rather, the color and brightness of the pupil area varies depending on the features of the eye and the ambient lighting. Correcting a red eye effect with a single color having a uniform brightness results in an unnatural appearance. Thus, when removing the red eye effect from a digital image using digital painting techniques, the touch-up of the image must be made in conformance with these varying color characteristics in order to achieve a corrected image that has a natural appearance.
There is a need for a digital imaging processing system in which digital painting techniques such as those described above and others can be applied to an image to correct a "red eye" effect without requiring either technical or artistic skills. Such a system would allow an unskilled user to remove a "red eye" effect from a photograph and replace it with a naturally appearing pupil area without requiring the aid of a specialist.